The present invention relates to a corrosion inhibitor for protecting metallic surfaces contacted with chloride-based de-icers.
Solid chloride salts such as sodium chloride and calcium chloride have been highly effective when used for removal of ice from highways. Unfortunately, chloride salts promote corrosion of metal. Consequently, the use of chloride salts enhances the corrosion of metals used as part of highways, such as bridges, signs and exposed reinforcing materials, as well as motor vehicles that use the highways.
Some chloride salts in solid form, particularly sodium chloride, suffer from a proclivity to bounce on pavement. Customary distributors for roadway distribution of solid salt, combined with the bouncing property of solid chloride salts can result in significant loss of ice melting capability from the scatter of solid salt off of the pavement surface. Chloride salts in liquid form offer advantages over solid chloride salts: a reduced chloride salt loading can be used per unit distance of pavement because losses off the pavement surface are minimized. The reduced chloride loading can be expected to yield beneficial secondary effects of lowered corrosion and reduced chloride levels in surface waters.
Efforts to minimize the corrosion of chloride de-icers have been ongoing for a number of years. Typical inhibitors such as amines, phosphate, zinc salts, borates, silicates and chromates are known and described. However, these attempts have led to limited success for a number of reasons, which include solubility problems of inhibitor, their toxicity and cost.
In recent years, attempts have been made to reduce the corrosive effects of chloride salt compositions, while maintaining the strong anti-freeze characteristics of these salts. U.S. Pat. No. 4,676,918 issued to Toth et al. discloses an anti-freeze composition comprising 20 to 90% by weight of a waste concentrate of the alcohol distilling industry in admixture with 10 to 80% by weight of water and optionally with additives. Similarly, U.S. Pat. No. 5,932,135 issued to Janke et al. discloses the use of at least 10% wine-making residue for use as a de-icing composition in combination with any of several chloride salts and at least 5% of water. Finally, U.S. Pat. No. 5,922,240 issued to Johnson et al. discloses the use of brewers' condensed solubles alone or in combination with at least one chloride salt. Further variations on the approach of adding organic waste to chloride salts include the ternary mixture of saccharinic acid, lignosulfonate and a chloride salt disclosed in U.S. Pat. No. 4,824,588 issued to Lin.
While each of the above compositions provides certain improvements in terms of reducing the corrosive effect of the chloride salts, they are still limited in that they draw from waste streams that produce only a fraction of the organic material needed for use with the huge amount of chloride salts which are applied in various anti-freeze applications. Since the organic materials proposed in the above disclosures are waste streams, their availability is subject to the demand for the primary product. Further, accessibility to alcohol distillates is limited in many of the northern regions where anti-freeze applications are most needed.
The States of Washington, Idaho, Montana and Oregon of the United States combined to establish a test for corrosion of chloride salts, and a specification for qualified pavement de-icing materials. The Pacific Northwest States (PNS) Coalition Chemical De-icer Specification limits the phosphorus and zinc content of de-icer materials. Hence, there is a need of an environmentally compatible, non-toxic, inhibitor effective for use with liquid de-icers.